#include<stdio.h>     
 #define N 515     
 char ch,s[N][N];     
 int v[N][N];     
 int main(){     
     int min,p,r1=0,r2=0,nr,n,m,i,j,h,x,y,x2,y2;     
     freopen("bmatrix.in","r",stdin);     
     freopen("bmatrix.out","w",stdout);     
     scanf("%d%d\n",&n,&m);     
     for(i=1;i<=n;++i){     
         for(j=1;j<=m;++j){     
             scanf("%c",&ch);     
             if(ch=='0')     
                 s[i][j]=1;     
             else     
                 s[i][j]=0;     
         }     
         scanf("%c",&ch);     
     }     
     for(j=1;j<=m;++j){     
         nr=0;     
         for(i=1;i<=n;++i)     
             if(s[i][j]==1)     
                 v[i][j]=++nr;     
             else{     
                 v[i][j]=0;     
                 nr=0;     
             }     
     }     
     for(i=1;i<=n;++i)     
         for(h=1;h<=m;++h){     
             nr=0;     
             min=v[i][h];     
             for(j=h;j<=m;++j){     
                 ++nr;     
                 if(v[i][j]<min)     
                     min=v[i][j];     
                 if(!v[i][j]){     
                     min=3;     
                     nr=0;     
                 }     
                 p=min*nr;     
                 if(p>r1){     
                     r1=p;     
                     x=i-min+1;        
                     y=j-nr+1;        
                     x2=i;        
                     y2=j;     
                 }     
             }     
         }     
     for(i=x;i<=x2;++i)     
         for(j=y;j<=y2;++j)     
             s[i][j]=0;     
     for(j=1;j<=m;++j){     
         nr=0;     
         for(i=1;i<=n;++i)     
             if(s[i][j]==1)     
                 v[i][j]=++nr;     
             else{     
                 v[i][j]=0;     
                 nr=0;     
             }     
     }        
     for(i=1;i<=n;++i)     
         for(h=1;h<=m;++h){     
             nr=0; min=v[i][h];     
             for(j=h;j<=m;++j){     
                 ++nr;     
                 if(v[i][j]<min)     
                     min=v[i][j];     
                 if(!v[i][j]){     
                     min=3;     
                     nr=0;     
                 }     
                 p=min*nr;     
                 if(p>r2)     
                     r2=p;     
             }     
         }     
     printf("%d\n",r1+r2);     
     fclose(stdin);     
     fclose(stdout);     
     return 0;        
}